There are several reasons you might see “undefined” in your Properties list throughout Mixpanel reports when segmenting:
The specific Property you’re segmenting by isn’t always sent along with the Event you’re analyzing. For example, let’s say you’re segmenting the Event “App Open” by the Property “Account type” If there are instances where App Open fires without the Account type Property getting sent with it, these will be categorized as “undefined” when you segment by Account type. Another common example is UTM parameters - “undefined” represents users who fired an Event without any UTM in the URL that brought the user to your site.
When segmenting an Event by a People Property, you’ll see “undefined” if there are People Profiles that don’t contain that Property or if the Event was triggered by a user without a People Profile at all. For example, let’s say you’re segmenting the Event “Song Play” by the People Property “Favorite Genre.” If there are Profiles that have triggered Song Play but don’t have the Favorite Genre Property, that value will be “undefined.” Triggers of Song Play by users without a People Profile will also show up under “undefined.”
Remove “undefined” from reports
If you don’t want to see “undefined” in your report, you can remove it by:
- Unchecking the “undefined” box or
- Looking only at instances where the Property in question “is set.”
If you’re getting “undefined” Property values but think you should not be, troubleshoot the issue using Live View. Click on Filter in the top left to look at Events coming in where the Property in question “is not set.” You can then use this data to look at your code and figure out why some Events are being fired without that Property.
Related Topic: Why do I see (No name), (NULL) or NaN values?